A cable tie or tie-wrap, also known as a hose tie, zap-strap or zip tie, is a type of fastener for holding items together, such as electric cables or wires. Because of their low cost and ease of use, tie-wraps are ubiquitous, finding use in a wide range of other applications. Stainless steel versions, either naked or coated with a rugged plastic, cater to exterior applications and hazardous environments.
The common tie-wrap, normally made of nylon, has a strap section with teeth that engages with a pawl in a head to form a ratchet so that, as the free end of the strap is pulled, the tie-wrap tightens and does not come undone. Another version of the tie-wrap allows a tab to be depressed to either adjust the tension or remove the tie-wrap. Another popular design of the cable tie locking mechanism involves a metallic barb in the head slot. The metallic, e.g. stainless steel, barb is inserted after the plastic part is molded. The barb engages and cuts into the strap surface to lock the strap in place when fastened.
Another prior-art design of a tie-wrap is assembled from a plastic strap component and a double lock head component. The plastic strap is extruded continuously and the head is fabricated separately and subsequently assembled to the strap. The double lock head has two slots with a metal barb in each slot to lock the plastic strap inserted into the head. The plastic material in this design is typically acetal.
This separate head and strap design is favored by industries, such as telecommunications, for securing large bundles of cables. The customer purchases strap material supplied on a reel, cuts a strap to a desired length, and secures the cut length of strap with a separate locking head comprising two metal barbs within a plastic housing.
A typical requirement for cable ties, in addition to, for example, chemical resistance to common automotive fluids, is that a fastened cable tie should withstand prolonged exposure to elevated temperatures, (e.g. at 125° C.), if it is to be applied, for example, in or in the vicinity of the engine compartment. At the same time, such a cable tie should show good mechanical strength at low, (e.g. sub-zero), temperatures. For such high-end applications, cable ties are often molded from a polyamide composition, (e.g. a plasticized polyamide 11 composition, an elastomer-modified polyamide 66 composition, etc.). Acetal material is also used to extrude cable tie straps and injection mold cable tie heads separately due to its relatively inferior processability.
A cable tie has several typical failure mechanisms. First, the cable tie strap can break when the fastening load is beyond the material strength limit. Another failure mechanism involves the unlocking of the strap from the cable tie head slot, whether the cable tie uses a plastic pawl or a metallic barb. Still another failure relates to creep, leading to loosening of cable bundles over time. Each failure mechanism can cause a cable tie to fail before reaching its designated loop tensile strength rating.
Since the original invention of the cable tie in 1958, many follow-up patents have emerged that mainly focus on improved manufacturing methods, new materials, or special applications. For example, for applications requiring high strength, stiffness, and environmental resistance, stainless steel cable ties have been developed. However, in many applications a nonmetallic solution is desired. Moreover, such stainless steel cable ties can be sharp, heavy, and may interfere with RF signals.
In such applications, more recent patents focus on reinforcing of the polymer matrix with graphene. Another prior art method of reinforcement involves introducing strengthening fibers into the raw plastic material prior to molding the cable tie. However, such reinforced plastics, when bought from a material supplier, tend to have a higher price than unreinforced plastics due to the additional step of compounding required during their manufacture. Such materials will furthermore increase the overall stiffness of the cable tie, rendering it incapable of being easily bent to form a loop.
It is also known from commonly owned PCT Application No. PCT/US16/27509 to form cable ties with a continuous glass reinforcing fiber positioned within the strap and/or head during an injection molding process. However, injection molding over glass fibers can be difficult to implement in a factory.
Accordingly, it would be desirable to provide a simple, inexpensive method for reinforcing the strength of a cable tie.